Thermal infrared imaging device is a device that converts infrared rays absorbed by an infrared absorption structure to heat and temperature changes caused by the heat convert electric signals. Thermal infrared imaging device are grouped into cooling type and non-cooling type. The non-cooling type infrared solid state imaging element devices without freezer can be miniaturized and are becoming cheaper intended to be accepted by consumer. Against this backdrop, the non-cooling type infrared solid state imaging devices that silicon PN diodes are used as temperature sensors to share the process of standard LSI are developed. On the other hand, temperature changes of the silicon PN junction diode are extremely smaller than the other temperature sensors such as vanadium oxide type. Therefore, it is necessary to reduce a noise of the silicon PN junction diode in order to improve S/N ratio in the non-cooling type infrared solid state imaging device. In addition, it is necessary that an infrared temperature sensor portion composed of an infrared absorption portion that incident infrared rays are converted to heat and a thermoelectric conversion portion is separated from the substrate which has large heat capacity to improve the heat sensitivity in the non-cooling type infrared solid state imaging device. Therefore, a part of the silicon substrate under the infrared temperature sensor portion is removed by etching to form a cavity.
In the conventional infrared solid state imaging device, the PN junction diodes of the temperature sensor portion are formed on a silicon substrate or an SOI (Silicon on insulator) substrate in which a buried insulation thin layer and a single crystal silicon layer formed on a substrate (supporting substrate) in order. The each individual diode is formed on the silicon or SOI layer and has a structure that one or more P type impurity regions and one or more N type impurity regions are formed in the vertical direction. Since a temperature change of the each individual diode is small, a plurality of diodes are connected in series to enhance sensitivity of the temperature sensor (for example FIG. 1 of the patent document 1). In the patent document 1, a temperature sensor in which contact holes are formed inside of active regions and buried electrodes are formed at the bottoms of the contact holes to connect the diodes so as to be reverse-biased in order to suppress 1/f noise is proposed.
[Prior Art Document]
[Patent Document]
[PATENT DOCUMENT 1] JP2005-9998